It is desirable to enable continuous drive and readout of the motion of an electromechanical device without the deleterious signal corrupting effects of parasitic feedthrough capacitance. Prior art electrostatic transducers employ parallel plate or comb drive electrostatic actuators which suffer from parasitic feedthrough capacitance. To mitigate feedthrough in prior art electrostatic transducers, methods are used such as modulating to a higher frequency, filtering the capacitive feedthrough out, and then demodulating back to baseband. Another method is to generate a cancellation current by inverting the drive signal and passing it through an external capacitor balanced with the parasitic feedthrough capacitance. Both of these methods require additional circuitry which may complicate the design of a micro-electro-mechanical system (MEMS) and are sensitive to environmental perturbations such as temperature induced shifts of the parasitic feedthrough capacitance.
The following references are incorporated by reference.
C. Acar and A. M. Shkel, “Post-release capacitance enhancement in micromachined devices and a method of performing the same,” U.S. Pat. No. 7,279,761 B2, 9 Oct. 2007 describe a prior art interdigitated comb drive structure which does not exhibit differential drive or feedthrough reduction.
O. Aydin and T. Akin, “A Bulk-Micromachined Fully Differential MEMS Accelerometer With Split Interdigitated Fingers,” IEEE Sensors Journal, vol. 13, no. 8, pp. 2914-2921, August 2013 describe prior art split interdigitated parallel plate structures which exploit differential changes in capacitance caused by a moving proof mass; however, they demonstrate no reduction in feedthrough.
S.-R. Chiu, C.-Y. Sue, L.-P. Liao, L.-T. Teng, Y.-W. Hsu, and Y.-K. Su, “A fully integrated circuit for MEMS vibrating gyroscope using standard 0.25 um CMOS process,” in Microsystems, Packaging, Assembly and Circuits Technology Conference (IMPACT), 2011 6th International, 2011, pp. 315-318 describe a differential MEMS gyroscope architecture, however feedthrough is not reduced by splitting of electrodes.
P. Shao, C. L. Mayberry, X. Gao, V. Tavassoli, and F. Ayazi, “JMEMS Letters A Polysilicon Microhemispherical Resonating Gyroscope,” Journal of Microelectromechanical Systems, vol. Early Access Online, 2014 describe feedthrough cancellation by inverting the drive signal with an op amp and passing through a capacitor to cancel feedthrough parasitic capacitance.
W. C. Tang and R. T. Howe, “Laterally driven resonant microstructures,” U.S. Pat. No. 5,025,346 A, 18 Jun. 1991 describe a prior art MEMS resonator of the type shown in FIG. 1, described below, which has capacitive feedthrough.
What is needed is a mechanism and method for actuating and detecting mechanical motion that greatly reduces or ideally cancels parasitic feedthrough signals which otherwise corrupt the measurements of prior art microelectromechanical (MEMS) devices. The embodiments of the present disclosure answer these and other needs.